This is a tree question but hope someone may have an answer. I live in Illinois & we're expecting Trillions of Cicadas in a few weeks. Can these bugs damage or even kill a 2 year old White Swamp Oak? If so, will wrapping the lower trunk only, in netting or burlap keep them out? Would I have to wrap the entire tree, which would be impossible for me as it's probably 15 feet tall. Thanks!

Cicadas lay eggs on the new tender twigs I believe. These eggs hatch and the young cicadas drop to the ground, burrow down and feed on the roots with their sucking mouthparts. So I do not think that wrapping a tree would in any way stop them.
Depending upon the type of cicada, their life in the soil is pre-programmed.
If I am not mistaken, the adult cicadas do not have functioning mouth parts. They simply emerge, along a staggered timeline to meet, mate and lay eggs for a new, future brood.

If you can't wrap the crown to protect twigs, you may get flagging.. later this summer you will see dead ends hang or broken off.
I don't think it kills trees, typically.

I agree.
Perhaps a severe infestation around a younger tree, might lead to noticeable damage. But to cause it's death might be extreme. Even in younger, newly planted trees.